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Mumps Cases and Outbreaks

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Mumps Cases

Mumps is no longer very common in the United States. From year to year, mumps cases can range from roughly a couple hundred to a couple thousand. For example in 2010, there were 2,612 cases, and in 2012, there were 229. Before the U.S. mumps vaccination program started in 1967, about 186,000 cases were reported each year. Since the pre-vaccine era, there has been a more than 99% decrease in mumps cases in the United States.

Number of mumps cases by year since 2010

Mumps Outbreaks

In some years, there are more cases of mumps than usual because of outbreaks. Mumps outbreaks can occur any time of year but often occur in winter and spring. A major factor contributing to outbreaks is being in a crowded environment, such as attending the same class, playing on the same sports team, or living in a dormitory with a person who has mumps.

MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease. Two doses of the vaccine are 88% (range: 66 to 95%) effective at protecting against mumps; one dose is 78% (range: 49% to 92%) effective. Outbreaks can still occur in highly vaccinated U.S. communities, particularly in close-contact settings. In recent years, outbreaks have occurred in schools, colleges, and camps. However, high vaccination coverage helps limit the size, duration, and spread of mumps outbreaks.

Past Mumps Outbreaks

In 2011-2013, there were several smaller mumps outbreaks reported on college campuses in California, Virginia, and Maryland. However, these all had limited spread, and national case counts for these years were at usual levels (several hundred cases per year).

In 2009 to 2010, two large outbreaks occurred.

One multi-year outbreak involved about 3,000 people and mostly affected high school-aged students who were part of a close-knit religious community in New York City and attended schools in which they had very close contact. The outbreak started when an infected student in this religious community returned from the United Kingdom where a large mumps outbreak was occurring.

The second outbreak involved about 500 people, mostly school-aged children, in the U.S. Territory of Guam.

In 2006, the United States experienced a multi-state mumps outbreak involving more than 6,500 reported cases. This resurgence predominantly affected college-aged students living in the Midwest, with outbreaks occurring on many different Midwestern college campuses.